(1) Field of the Invention
The present invention relates to determining the appropriate spacing between fixed-wing aircraft arriving at runways so as to permit the minimum separation commensurate with safe operation as a function of the atmospheric conditions. More specifically, this invention is directed to a vortex advisory system which will enable flight controllers to vary the separation between aircraft as a function of the accurately predicted motion of wake vortices produced by the aircraft. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
Aircraft generating lift create a pair of counterrotating cylindrical air masses known in the art as wake vortices. In a homogeneous quiet atmosphere the vortex pair will descend to an altitude of about half a wingspan above the ground and then the individual vortices will separate and move apart roughly parallel to the ground. However, in the presence of winds, the vortices are convected. Thus, the self-induced motion of the vortices near the ground may be cancelled by the motion which would be attributable to the surface wind thus resulting in the stalling of a wake vortex generated by a first aircraft in the flight path of a following aircraft.
The phenomenon of aircraft wake vortices has been known since the beginning of powered flight, but the potential dangers associated with encountering wake vortices has only recently become apparent. An aircraft which inadvertently encounters a vortex can be subjected to rolling moments exceeding the roll control capability. A dangerous loss of altitude or structural failure can also result. The chance of a vortex encounter is, of course, greatest at airport terminal areas where numerous aircraft will be following the same flight path in approaching the terminal and aircraft on approach have little time and altitude to recovery from the effects of a vortex encounter. The potentially disastrous results incident to an unexpected wake vortex encounter are greatest in those areas where light and heavy aircraft operate in close proximity.
In order to prevent aircraft-vortex encounters, the Federal Aviation Administration has established separations between aircraft, based on aircraft type, which are greater than those which testing has indicated as being the minimum required for vortices to decay in strength to a point where they are no longer harmful or for vortices to move laterally away from the flight path of a following aircraft. These separations, however, decrease the capacity of the airport system. In an effort to increase the capacity of operation into high density air terminals, by reducing approach separation times, resort has been had to two diverse approaches. On the one hand, considerable research has been conducted on methods to hasten the demise of vortices at the source by modifying aircraft through the use of devices such as wing spoilers, mass injectors, wing-tip modifications and the deployment of trailing devices. Conversely, significant attention has been directed to means for reliably locating and tracking vortices. Such tracking means are exemplified by the apparatus disclosed in U.S. Pat. No. 3,693,015 and have been characterized by a lack of predictive capability and the need for complex specifically designed hardware.
A further problem facing flight controllers; i.e., a task in addition to instructing the aircraft under his control to maintain a specific spacing depending on aircraft type, lies in the requirement that the aircraft crew be advised of wind direction and speed. At the present time the controller must refer to moving needle-type instruments and must mentally integrate the movements of the instrument pointers over a period of, for example, one minute. The information transmitted to the flight crew is thus average wind speed and direction, measured at only one point on the airfield, and transient conditions such as wind gusts will enter into the mental calculation of the average. The potential for inaccuracy is obvious and is increased by the fact that there can be substantial variation in the average wind conditions such as, for example, between landing and take-off runways.